The body mass index (BMI)

The body mass index (BMI), or Quetelet index, is a measure of relative weight based on an individual’s mass and height.

Devised between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing “social physics”,[2] it is defined as the individual’s body mass divided by the square of their height – with the value universally being given in units of kg/m2.

\mathrm{BMI} = \frac{\text{mass}(\text{kg})}{\left(\text{height}(\text{m})\right)^2}
\mathrm{BMI} = \frac{\text{mass}(\text{lb})}{\left(\text{height}(\text{in})\right)^2}\times 703 

The factor for Imperial or US customary units is more precisely 703.06957964, but that level of precision is not meaningful for this calculation.

BMI can also be determined using a table[note 1] or from a chart which displays BMI as a function of mass and height using contour lines, or colors for different BMI categories, and may use two different units of measurement.[note 2]

The BMI is used in a wide variety of contexts as a simple method to assess how much an individual’s body weight departs from what is normal or desirable for a person of his or her height. There is however often vigorous debate, particularly regarding at which value of the BMI scale the threshold for overweight and obese should be set, but also about a range of perceived limitations and problems with the BMI.

Even though many other differently calculated ratios have been invented,[note 3] others haven’t been used as often.